Technics SU-V97 Service Manual Schematic

[Alfredo Abate]

I'm attempting to fix a Technics SU-V97 amplifier for a friend. Would anyone have a copy of the service manual or schematic?

 

[century tek]

I haven't looked but hifi engine might have a schematic for you. If I might ask, what is the problem?

 

[PE9ZZ]

No, they only have SU-V98 which is very different. Found a Youtube clip of it being opened and tested. Bit of a crappy cheapo amp, I concur with the Youtuber...

Edit: And a photo copy.

Tjerk, 9ZZ

 

[Alfredo Abate]

Yeah I scoured the internet looking for this information on this amplifier before posting. I saw the one video that PE9ZZ mentioned as well as a few sellers that had the service manual. HiFi engine didn't have it or anything that was similar.

The issue is the right channel is distorted at any volume. The left channel is perfectly clear. Plugging in headphones yields the same results (distorted right channel). I've cleaned all the switches, sliders, etc with Deoxit which didn't make any difference. I did a visual inspection to see if anything looked awry but didn't find anything. That's as far as I got before I decided to start looking for the schematic.

Thanks.

 

[SVI2004A]

No, they only have SU-V98 which is very different. Found a Youtube clip of it being opened and tested. Bit of a crappy cheapo amp, I concur with the Youtuber...

Edit: And a photo copy.

Tjerk, 9ZZ

That YouTube user has a chip on the shoulder bigger than the one on its heatsink...

 

[SVI2004A]

ahh SVI2105

 

[PE9ZZ]

The issue is the right channel is distorted at any volume. The left channel is perfectly clear.

Schematic's not going to help you. The whole amplifier consists of the SVI2105 module. If one channel in it is borked you have to replace the whole chip. You could try to swap the inputs on it to see if the fault stays at the same channel. Having said that, I've had cases of bad output relays that would create audible distortion. However, that usually went away when only using headphones. Also, replacement modules aren't that expensive:


Tjerk, 9ZZ

 

[SVI2004A]

Think I have some manual w/ same power IC - can check set for correct operation..... often pre drive transistors 2SA1123 (and in computer drive versions Current Stabilisers 2SC2631) often wreak this havoc


Essentially this ic is a carry on of SVI2000 - with speaker protect/mute ic inbuilt (predecessing SVI3104 onward to SVI3206)

Here is a screenshot of power amp specifics.... *** they screwed up on voltages***

Pins 1,2,3,4... 20, 19,18,17 are correct.... pins 5 and 16 should be -1.8V





Certainty is outer 5 pins have identical function to SVI2003/SVI2004



So pin 1 and 1 are same.......
And pin 20 (on 2100) and pin 16 (on 2000) are same

Work inward on either... the outer 5 are identical

 

[SVI2004A]

Schematic's not going to help you. The whole amplifier consists of the SVI2105 module. If one channel in it is borked you have to replace the whole chip. You could try to swap the inputs on it to see if the fault stays at the same channel. Having said that, I've had cases of bad output relays that would create audible distortion. However, that usually went away when only using headphones. Also, replacement modules aren't that expensive:
View attachment 1685312

Tjerk, 9ZZ

Not the whole amp.... it’s a stereo DPP, have AN7062 V amp and driver transistors.

 

[Alfredo Abate]

Below are the voltages of the SVI 2105. I haven't checked the transistors yet.

1 1.8
2 61.2
3 -0.005
4 -61.2
5 -1.80
6 -0.005
7 0
8 -0.002
9 0
10 -0.046
11 -4.33
12 -14.97
13 -14.10
14 -14.95
15 -0.005
16 -1.32
17 -61.5
18 -0.005
19 61.5
20 1.54

 

[Alfredo Abate]

I checked the following transistors using the diode function on my DMM. They all appear to be checking okay.

Q71 A1123
Q72 A1123
Q401 C1685
Q402 A992
Q501 C2631

 

[PE9ZZ]

Test the speaker relay. Short the contacts for R_Ch and see if the distortion disappears. If it doesn't: new module.

Tjerk, 9ZZ

 

[Alfredo Abate]

Test the speaker relay. Short the contacts for R_Ch and see if the distortion disappears. If it doesn't: new module.

Tjerk, 9ZZ

I did remove the relay, opened it up, and clean the contacts well. They looked pretty good before I started. I re-soldered the relay back into the place but the issue still remains.

I'm not sure which side is for the right channel to attempt the short. Will either side be okay to do this? Also, can you confirm which pins I would need to short? I forgot to snap a picture of the bottom of the relay.

Thanks.

 

[PE9ZZ]

That's easily figured out. Hook one lead of your multimeter set to continuity beeper to R_Ch speaker out and jab the pins of the relay. The pad where your meter beeps (NO) should be shorted to the pad next to it (COM). That one is connected to the SVI module. The third pin (NC) of the relay is not connected (I expect) and just sticks through the board. BUT if you cleaned the relay it looks like it's innocent and the module is borked. Still, no harm in ruling out the relay.

Tjerk, 9ZZ

 

[SVI2004A]

A CRO would help

But yes, it’s possible that bias control in the IC or a driver transistor is on the fritz

Iirc Pins 16-20 in your set are Rch - and the readings you have on 16 (-1.32) and 20 (1.54) seem low compared to the healthy Voltages on pins 1 and 5

I have seen 2SA1123s cause this distortion.... from memory there’s 2 resistors in series as current stabiliser / bootstrap (example R410 and R408 in 2nd schematic)
Check they’re also in tolerance.

There’s no known counterfeit of SVI2105, they’re out there - most seem to be pulls - there svi2105B (BC power module)